What Does "pH" Stand for in a Chemical Formula?

Related Articles

A chemical formula uses the elements of a solution to express what it is. The formula then may be used to determine the properties of the solution and thereby predict how it will behave under a variety of circumstances. The term "pH" is used within chemical formulas to indicate the presence of hydrogen. The "H" means hydrogen in this formula, just as the "H" in "H2O" indicates the presence of hydrogen in water -- two atoms of hydrogen and one atom of oxygen.

What pH Stands For

The term "pH" is used to mean the power of hydrogen within the solution. There is some debate within the scientific community of where the "p" comes from, but it now is indicative of the word "power." It indicates the molar concentration of hydrogen ions within the solution and measures the acidity or alkalinity -- also called the base -- of the solution. The pH level is measured on a negative base-10 logarithm.

How pH Is Used in Chemical Formulas

Using the example of water, a few of the water molecules break apart, or disassociate. Some of the molecules give up an atom of hydrogen, becoming hydroxyl ions. These are expressed in a chemical equation as OH-. These hydroxyl ions join with water molecules to make hydronium ions, expressed as H3O+. Hydronium ions simply are called hydrogen. If the water is pure, the amount of hydrogen and hydroxyl ions are equal. This solution is neither acidic nor alkaline; therefore, it is neutral and carries a pH number of 7. Acidic substances give up hydrogen ions and alkaline substances take on hydrogen ions.

The pH Negative Logarithm

A solution that is heavily acid can have one hundred trillion -- 100,000,000,000,000 -- times as many hydrogen ions as an alkaline solution. To be able to deal with these huge numbers, scientists use a logarithmic scale known as the pH scale. Each number on the scale indicates a change of 10 times the concentration of hydrogen ions in the solution. This way, you don’t have to work with the huge number of zeros involved in figuring an equation without the logarithmic scale. The scale ranges from 0 to 14. The pH is the negative logarithm of the concentration of hydrogen ions in the solution. It is expressed as pH = log 1/[H+ = −log [H+]]. The bracket around the H+ indicates hydrogen concentration. The equation means that for each pH number change (up or down), the concentration of hydrogen ions changes tenfold.

References

About the Author

Suzy Kerr graduated from Grady School of Journalism and Mass Communications at the University of Georgia. She completed her Master's degree in Nutrition Sciences, also at the University of Georgia. Suzy has been a successful health, fitness and nutrition writer for more than 10 years, and has been published in various print and online publications.